The application generally relates to a controller for an AC motor. The application relates more specifically to a controller for an AC motor with integrated metering functions to measure, store and communicate data suitable to verify the energy saving performance of the controller.
Alternating current (AC) motors are major consumers of electricity in the U.S. accounting for over 60% of the nation's electricity consumption. The U.S. Department of Energy estimates that improved control systems for AC motors in pump, fan, and compressed air systems could save nearly 15,000 gigawatt-hours per year and potentially $900 million per year in energy savings. The potential to obtain such energy savings has resulted in the promotion of “high efficiency” and “premium efficiency” AC motors for use in many applications. “High efficiency” and “premium efficiency” are terms used by motor manufacturers to describe motors conforming to the minimum efficiency standards instituted by the National Electrical Manufacturers Association (NEMA) and described in various Energy Policy Acts passed by the U.S. Congress. “High efficiency” and “premium efficiency” motors can typically cost 10-25% more than standard motors while providing, in general terms, several percentage points higher efficiency than standard motors under rated load. Alternatively, energy savings can be obtained by reducing the electricity consumption of existing AC motors. In facilities that use many AC motors, the potential energy savings to be obtained by reducing the electricity consumption of each motor at the facility can be substantial.
AC motor controllers and drives, such as a variable speed drive (VSD), a variable frequency drive (VFD), and variable load controller (VLC), can be designed to reduce the electrical power and energy consumption of AC motors. However, the cost for an AC motor controller or drive and the corresponding labor to install such a device could easily cost hundreds of dollars for a single-phase, fractional horsepower (HP), e.g., ½ or ¼ HP, motor, and thousands of dollars for a three-phase, large HP, e.g. 50 HP, motor. Therefore, an economic analysis should be performed to understand whether the potential savings to be obtained from an AC motor controller or drive can justify the cost associated with installing an AC motor controller or drive.
An effective economic analysis of an AC motor requires the collecting of electric power and energy consumption data for the AC motor prior to the installation of an AC motor controller or drive to establish a baseline condition for the AC motor. The effective economic analysis of the AC motor also requires the continuous monitoring of the electric power and energy consumption of the same AC motor after the installation of the AC controller or drive. In addition to being used in an economic analysis of the AC motor, data collection is also useful to support utility incentives and rebates associated with energy savings or reduced power consumptions of the AC motor.
While data collection is a significant part of an effective economic analysis of an AC motor, the data collection part of the analysis has historically been expensive and time consuming. The cost of the data collection function has to be included in the economic analysis of the motor in order to obtain meaningful results. Often, data collection is only performed on a representative sample of a particular type of AC motor and for a representative period. For AC motors used in applications with varying loading conditions, changes in the operation of the AC motor from the change in loading conditions may render the one-time collected data on the AC motor obsolete and inappropriate for analysis.
Therefore what is needed is a system and method that can collect, store and transmit data regarding the operation of the motor for energy savings analysis and can re-establish baseline conditions for the motor in response to changes in loading conditions or operating conditions for the motor.